1. Field of the Invention
The present invention relates to an artifical tooth which is formed of a porcelain or synthetic resin material. The artifical tooth is particularly designed for a molar tooth suitable for the preparation of a partial denture.
2. Background of the Invention
In dentistry, a full or partial denture has been put in the mouth for making up for a full or partial loss of teeth with a view to recovering the appearance or the decline of functions (such as mastification and pronunciation) resulting from such a loss.
In particular, partial dentures are most frequently used to cover a variety of cases from a loss of one tooth to the presence of one tooth left. In general, such partial dentures compose a retainer, a connector, a denture plate, and an artifical tooth or teeth. When preparing the partial dentures, attention should be paid to biological particulars in the design of the retainer and the connector. In the selection and alignment of artificial teeth, attention also has to be paid to the appearance thereof and to the recovery of functions (such as mastification and pronunciation). In the selection and alignment of artifical teeth, therefore, special regard must be paid to the size, form, color tone, vertical height, location, proximal consideration, occlusal consideration, and so on of the artifical teeth, depending upon the state of the remaining tooth or teeth.
However, since the conventional artifical teeth have usually been designed and made with full dentures in view, suitable artificial teeth selected from such teeth made for full dentures have been used to make partial dentures. As illustrated in FIG. 7, one of the conventional artifical teeth designed for use with full dentures is slightly bent in the buccolingual direction. Hence, this tooth should be used in combination with a retainer, a connector, and a metal plate, when preparing a partial denture. In this case, it is inevitably required that the basal and proximal surfaces of the tooth be partly removed by cutting. As a result, not only is much time required for the preparation of a partial denture, but the contour and appearance of the artifical tooth are deteriorated. This operation thus gives an operator a great deal of trouble.
To solve such a problem, Japanese Utility Model Publication No. 37-2475 proposes an artificial tooth for the preparation of a partial denture, which has its basal surface provided at the center with a concave dent. According to the teachings disclosed therein, the proximal surface adjacent to that concave dent is formed with an elongate retaining groove extending from the bottom of the basal surface thereof, and a small dent of a relatively large size is formed above the groove for the insertion of a retainer.
However, the artificial tooth disclosed in Japanese Utility Model Publication No. 37-2475 is formed so that its basal surface is only provided at its center with the concave dent, and it has a contour similar to that of an ordinary natural tooth except for the elongate retaining groove extending from the bottom of the basal surface of the proximal surface and the small dent of a relatively large size formed above the groove. Hence, the retainer, the connector, and the projections from the metal plate are often located below the lingual side of the artificial tooth. In many cases, therefore, the lingual lower portion of the artificial tooth must be removed by cutting to a large extent. With this artificial tooth, a significant reduction in the amount of operation to be conducted by an operator is still not achieved. Besides, a denture having a sufficient stable strength still cannot be prepared, since a synthetic resin-made dental plate cannot be firmly filled in the central concave dent due to the fact that the central concave dent in the basal surface is, for the most part, surrounded by the side walls of the artificial tooth.
Further, this known artificial tooth offers problems in connection with stability and a wearer's load, when used as a partial denture, on the lower structure of which a larger pressure is applied, as compared with an ordinary full denture, since no regard is paid at all to the form of the occlusal surface thereof.